How to Combine array_diff_ukey and array_map in PHP for Advanced Array Key Comparison

In PHP array operations, common functions like array_diff, array_diff_assoc, and array_diff_key provide
set difference comparisons for array values or keys. However, when we need to introduce custom rules in key comparison logic,
array_diff_ukey becomes very useful. It allows developers to pass a user-defined callback function to determine
the ordering of two keys during comparison.

For example, suppose we have two arrays:

</span><span><span class="hljs-variable">$array1</span></span><span> = [
    </span><span><span class="hljs-string">"User_01"</span></span><span> => </span><span><span class="hljs-string">"Alice"</span></span><span>,
    </span><span><span class="hljs-string">"User_02"</span></span><span> => </span><span><span class="hljs-string">"Bob"</span></span><span>,
    </span><span><span class="hljs-string">"User_03"</span></span><span> => </span><span><span class="hljs-string">"Charlie"</span></span><span>
];

</span><span><span class="hljs-variable">$array2</span></span><span> = [
    </span><span><span class="hljs-string">"user_1"</span></span><span> => </span><span><span class="hljs-string">"Alice"</span></span><span>,
    </span><span><span class="hljs-string">"user_4"</span></span><span> => </span><span><span class="hljs-string">"David"</span></span><span>
];
</span></span>

By default, array_diff_ukey does not recognize the similarity between "User_01" and "user_1".
If business logic requires us to compare them, we need to use
array_map for preprocessing.

Normalizing Keys with array_map

We can use array_map along with array_keys to “normalize” array keys into a consistent format before comparison:

<span><span><span class="hljs-function"><span class="hljs-keyword">function</span></span></span><span> </span><span><span class="hljs-title">normalizeKey</span></span><span>(</span><span><span class="hljs-params"><span class="hljs-variable">$key</span></span></span><span>) {
    </span><span><span class="hljs-comment">// Remove underscores and convert to lowercase</span></span><span>
    </span><span><span class="hljs-keyword">return</span></span><span> </span><span><span class="hljs-title function_ invoke__">strtolower</span></span><span>(</span><span><span class="hljs-title function_ invoke__">str_replace</span></span><span>(</span><span><span class="hljs-string">"_"</span></span><span>, </span><span><span class="hljs-string">""</span></span><span>, </span><span><span class="hljs-variable">$key</span></span><span>));
}

</span><span><span class="hljs-variable">$normalized1</span></span><span> = </span><span><span class="hljs-title function_ invoke__">array_combine</span></span>(
    </span><span><span class="hljs-title function_ invoke__">array_map</span></span><span>(</span><span><span class="hljs-string">"normalizeKey"</span></span><span>, </span><span><span class="hljs-title function_ invoke__">array_keys</span></span><span>(</span><span><span class="hljs-variable">$array1</span></span><span>)),
    </span><span><span class="hljs-title function_ invoke__">array_values</span></span><span>(</span><span><span class="hljs-variable">$array1</span></span><span>)
);

</span><span><span class="hljs-variable">$normalized2</span></span><span> = </span><span><span class="hljs-title function_ invoke__">array_combine</span></span><span>(
    </span><span><span class="hljs-title function_ invoke__">array_map</span></span><span>(</span><span><span class="hljs-string">"normalizeKey"</span></span><span>, </span><span><span class="hljs-title function_ invoke__">array_keys</span></span><span>(</span><span><span class="hljs-variable">$array2</span></span><span>)),
    </span><span><span class="hljs-title function_ invoke__">array_values</span></span><span>(</span><span><span class="hljs-variable">$array2</span></span><span>)
);
</span></span>

At this point, the keys of $normalized1 and $normalized2 have been converted to a “lowercase without underscores” format.

Using array_diff_ukey for Advanced Comparison

Next, we can use array_diff_ukey to perform the comparison:

<span><span><span class="hljs-variable">$result</span></span><span> = </span><span><span class="hljs-title function_ invoke__">array_diff_ukey</span></span><span>(</span><span><span class="hljs-variable">$normalized1</span></span><span>, </span><span><span class="hljs-variable">$normalized2</span></span><span>, function(</span><span><span class="hljs-variable">$a</span></span><span>, </span><span><span class="hljs-variable">$b</span></span><span>) {
    </span><span><span class="hljs-keyword">return</span></span><span> </span><span><span class="hljs-title function_ invoke__">strcmp</span></span><span>(</span><span><span class="hljs-variable">$a</span></span><span>, </span><span><span class="hljs-variable">$b</span></span><span>);
});

</span><span><span class="hljs-title function_ invoke__">print_r</span></span><span>(</span><span><span class="hljs-variable">$result</span></span><span>);
</span></span>

The output is:

<span><span>Array
(
    [</span><span><span class="hljs-meta">user02</span></span><span>] => Bob
    [</span><span><span class="hljs-meta">user03</span></span><span>] => Charlie
)
</span></span>

As we can see, User_01 and user_1 are recognized as the same key and excluded from the difference result.

Conclusion

By combining key normalization with array_map and custom key comparison with array_diff_ukey,
we can handle more complex key matching logic, such as ignoring case, removing specific characters, or even partial matches.
This approach is especially useful when dealing with external data sources (like API responses or user-uploaded data), as their keys often do not maintain a consistent format.

This flexible combination of functions not only improves code maintainability but also helps us quickly adapt to changing data structures.

<span></span>

• Related Tags:

  array_map